I distinctly remember one of the novels implying that the "slingshot effect" was something only Starfleet knew about, and that it was secret. Kirk knew about it, of course, because he utilized it both by accident and on purpose for a Starfleet assignment in TOS. But because pinpoint accuracy is required, and the maneuver extremely hazardous, it wasn't a reliable means of time travel.

We could just as well decide the heroes simply stopped doing it; nothing indicates they would be unable to do it. Picard and Riker in "Time Squared" discuss time travel as a known quantity:

Picard: "What force or phenomenon could cause the shuttle to be thrown back in time?"
Riker: "None that we've encountered. In theory, accelerating beyond warp 10."
Picard: "Using the gravitational pull of a star to slingshot back in time. Is that what happened here?"

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It sounds as if

a) the TNG heroes have encountered several all-new time travel techniques themselves
b) none fit the specs of this particular incident
c) the underlying concept of time travel in Newtonian space is that you travel faster than infinitely fast - so you arrive before you left - and Riker refers to this, half in jest
d) slingshotting is a different way to time travel, and one Picard seriously considers, but doesn't fully accept as the answer to the mystery of the day.

Overall, though, time travel in TNG, DS9 or VOY is mundane and treated matter-of-factly.

This is in sharp contrast with, say, natural phenomena that travel at warp (often seen in TOS and retroactively in ENT, but emphatically declared an unknown quantity or an impossibility in TNG) or dark rifts in space (something Kirk met in "Immunity Syndrome" but Data in "Where Silence Has Lease" describes as previously unencountered)...

I distinctly remember one of the novels implying that the "slingshot effect" was something only Starfleet knew about, and that it was secret. Kirk knew about it, of course, because he utilized it both by accident and on purpose for a Starfleet assignment in TOS. But because pinpoint accuracy is required, and the maneuver extremely hazardous, it wasn't a reliable means of time travel.

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You're probably thinking of my recent novel Department of Temporal Investigations: Forgotten History. It explains why the slingshot effect is a dangerous maneuver and one that not all ships are capable of achieving. There is precedent for this; "Tomorrow is Yesterday" showed that the ship was pretty banged up by the slingshot and barely came through it intact. "Assignment: Earth" didn't show the actual slingshot in either direction, so it could've been equally hazardous. TVH didn't show it as being quite so turbulent, but it wasn't easy either; Spock had to get the computations just right to pull it off.

It just seems like post TOS, unless using the exact means they used to get there (Borg tachyon hole, the wormhole in "Yesterday's Enterprise") then they're stuck.

Looking at Memory Alpha, this would seem to be the best answer: Ronald D. Moore commented: "I would assume that the precise calculations involved in using the slingshot method are something of a closely-guarded secret."

So basically, probably only Spock knows how to do it. I can buy that.

Picard's line means that it can be done is probably public knowledge given there were hundreds of Enterprise crew, so it can't be "Captain's eyes only"

The fact that they were able to do it in a beat up looking Bird of Prey means its not "Enterprise only". I'm going with Moore here.

"Tomorrow is Yesterday" showed that the ship was pretty banged up by the slingshot and barely came through it intact.

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Or then it could be argued that both this and ST4 featured the exact same risk: the crew loses consciousness and therefore risks letting the ship get wrecked (say, by slamming into an atmosphere), but damage as such is not inevitable at all.

Once the risks are known, preparing for the loss of consciousness and taking precautions regarding the unsupervised arrival at the destination is easy enough, allowing our heroes to conduct the "Assignment: Earth" mission without damage.

It just seems like post TOS, unless using the exact means they used to get there (Borg tachyon hole, the wormhole in "Yesterday's Enterprise") then they're stuck.

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I'm not sure I can recognize any good examples of this. In "Yesterday's Enterprise", the heroes were starved of means to do anything much; flying the E-C to a star, let alone completing a slingshot maneuver and then somehow returning to Narendra III, seemed well beyond their capabilities. In all other TNG time travel stories, the heroes were up the timecreek not just without a paddle, but without a canoe as well: you can't slingshot if you don't have a starship!

When time travel took place in a way that involved a starship, there wasn't really an incentive to escape from the situation by slingshotting: the heroes had a task to accomplish first. Say, in "Trials and Tribble-ations", they have to hunt down Arne Darvin before they can go home. Also, the means of getting into the past is usually also the logistically most convenient for subsequent travel in that situation. In "Past Tense", slingshotting with the Defiant to locate the missing people would have taken much more effort (and time!) than using the means-of-the-week, especially as they had to do it repeatedly - and were chasing after somebody who had used the means-of-the-week in the first place, so following the spoor made perfect sense.

There are plenty of occasions where time travel would have made sense as a means of "rewinding the clock" to compensate for the fact that the heroes arrived too late. But using it to compensate for time travel that had already occurred was generally not tactically necessary or desirable.

Picard's line means that it can be done is probably public knowledge given there were hundreds of Enterprise crew, so it can't be "Captain's eyes only"

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Swearing the hundreds of Kirk's crew to silence would keep it from becoming public knowledge for all eternity afterwards, though. And the exchange between Picard and Riker certainly didn't indicate that others aboard Picard's ship would be in the know: rank hath its privileges.

Of course, the real life reason is that an easily achievable undo button robs any story of consequence or tension, so they just pretended it didn't exist.

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Indeed, the TOS crew had enough arcane knowledge to screw up most stories.

(1) They knew that traversing the galactic barrier produces Q-like powers in "espers" (Where No Man Has Gone Before). Granted, espers became super-powered dickwads, but if they were really up against it, they could do it by warping out to the galaxy's edge.

(2) They could simply synthesize a potion to give them the ability to conjure tremendous telekenetic abilities (Plato's Stepchildren - recall that these powers were used with great effect on the orbiting Enterprise).

(3) They could synthesize a potion to allow them to live and act at tremendously high speed (Wink of an Eye). Sure would come in handy during a crisis.

(4) They could time travel at will (Assignment: Earth).

(5) They stole a cloaking device, which they never used again (Enterprise Incident).

So there it is, they could go backwards in time, speed up time and run circles around enemies, create pyschic powers at will which would allow them to hold starships stationary in space, and they could make their ship invisible.

Sorry, but if I am captain of the Enterprise, I am reaching into that bag of tricks when I meet the next big bad.

The novel DTI: Forgotten History goes into detail about this, and explains why so few people know of the technique (and even fewer are able to use it) in the Next Generation era.
In short...

Only the old Enterprise could do it, due to some kind of strange alteration her engines went through during the original series. Only a few members of the old crew knew how to reproduce this change.

Of course, the real life reason is that an easily achievable undo button robs any story of consequence or tension, so they just pretended it didn't exist.

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There is a unique phenomenon the Enterprise experienced fairly early on - the "cold start" in Naked Time. As Spock said, it stemmed from a theory on the relationship between time and antimatter.

While certainly a slow way of time travel, it may have prepped the engines enough to allow the slingshot effect to happen in Tomorrow is Yesterday. But did the crew then do this as well to the Klingon Bird Of Prey in The Voyage Home?

(1) They knew that traversing the galactic barrier produces Q-like powers in "espers" (Where No Man Has Gone Before). Granted, espers became super-powered dickwads, but if they were really up against it, they could do it by warping out to the galaxy's edge.

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I wouldn't sweat this one, as the ratio of empowering/fatalities is a low one even when one has suitable espers aboard. The ratio of effects/no effects seems to be low as well: two times out of three, nothing much happens when our heroes go through the Barrier. In a crisis, those odds would do nobody any good, even assuming the crisis would allow one to take the time to go to the Barrier and back.

(2) They could simply synthesize a potion to give them the ability to conjure tremendous telekenetic abilities (Plato's Stepchildren - recall that these powers were used with great effect on the orbiting Enterprise).

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The substance kironide itself was well known to our heroes, as was it's metabolic behavior in the body, but the telekinetic effects were a surprise; apparently, they do not normally manifest when people digest kironide.

Either the substance interacts with local tri-isopseudic fields, and when you move muscles saturated with it, you can manipulate those fields - which then manipulate other things saturated with or covered in kironide. But only on Platonius.

Or then the substance just makes you crazy as a cuckoo and you start to think that you are doing telekinesis, dancing, kissing, or pulling starships from the sky.

(3) They could synthesize a potion to allow them to live and act at tremendously high speed (Wink of an Eye). Sure would come in handy during a crisis.

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Possibly. But the story-ruining potential isn't all that great... Remember the caveat that the body wears down real quick. Combine that with the fact that even if you move very fast, things like doors or guns around you will not do so, unless you also swallow another potion that gives you superhuman strength - and you begin to look for other ways to run rings around your enemy.

(4) They could time travel at will (Assignment: Earth).

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Which probably did quickly put a stop not just to drama and tension, but to everything else as well, bringing about the end of the universe, and resulting in things being reset...

(5) They stole a cloaking device, which they never used again (Enterprise Incident).

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After this episode, the heroes did not exactly encounter situations where they would have wanted to hide their starship. Spinoff shows and movies got mileage out of the device, though.

There is a unique phenomenon the Enterprise experienced fairly early on - the "cold start" in Naked Time. As Spock said, it stemmed from a theory on the relationship between time and antimatter.

While certainly a slow way of time travel, it may have prepped the engines enough to allow the slingshot effect to happen in Tomorrow is Yesterday. But did the crew then do this as well to the Klingon Bird Of Prey in The Voyage Home?

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The book does explain how Spock discovers the means to alter other vessels' warp cores and coils to create the necessary temporal effects. But it's not information that's widely disseminated. And there are Federation laws restricting time travel.

I thought they turned that cloaking device over to the Feds. I thought that was the whole point.

As for Post TNG eps where a crew was stuck after time-travelling. I was also thinking of the Bozeman, but the circumstances of their arrival is so damn confusing...and seems to be a predestination one as the universe doesn't change ala' "Yesterday's Enterprise"...sending them back would probably be too dangerous.

The novel DTI: Forgotten History goes into detail about this, and explains why so few people know of the technique (and even fewer are able to use it) in the Next Generation era.
In short...

Only the old Enterprise could do it, due to some kind of strange alteration her engines went through during the original series. Only a few members of the old crew knew how to reproduce this change.

Of course, the real life reason is that an easily achievable undo button robs any story of consequence or tension, so they just pretended it didn't exist.

Click to expand...

There is a unique phenomenon the Enterprise experienced fairly early on - the "cold start" in Naked Time. As Spock said, it stemmed from a theory on the relationship between time and antimatter.

While certainly a slow way of time travel, it may have prepped the engines enough to allow the slingshot effect to happen in Tomorrow is Yesterday. But did the crew then do this as well to the Klingon Bird Of Prey in The Voyage Home?

Click to expand...

That would make a lot of sense that the Enterprise engines were already running a unique intermix which allowed them to accidentally time-travel with the slingshot maneuver in "Tomorrow is Yesterday" and no other ships accidentally have done so in the same manner. That way, only certain knowledgeable people like Spock or Scotty could modify the BOP engines to do the same thing while other ships don't have this ability.

. I was also thinking of the Bozeman, but the circumstances of their arrival is so damn confusing...and seems to be a predestination one as the universe doesn't change ala' "Yesterday's Enterprise"...sending them back would probably be too dangerous.

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Who says the Bozeman wasn't sent back eventually?

On the other hand, why bother? People traveling to the future aren't changing the past in the general case; nobody will miss them if they don't return, either because the future they end up in is the one in which they originally went missing, or because time "self-heals" minor things like that. And changing the past is the only thing our heroes ever worry about - insofar as changing it affects the quality of life in the present.

That way, only certain knowledgeable people like Spock or Scotty could modify the BOP engines to do the same thing while other ships don't have this ability.

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So the mission to observe Earth in the 1960s was so super-secret that not even all that many in Starfleet were told of it?

Sounds a bit dubious, when we think how unimportant that mission appeared. Our heroes didn't exactly achieve anything they could plausibly have set out to achieve - they just had random adventures in the past. Why study the 1960s? There must be mysteries a thousand times more interesting, in time periods where fewer things can go horribly wrong. Say, before the invention of high-power radars, or optical telescopes...

The episode makes it sound as if time travel is mundane and technologically uninvolving, and is applied on trivial pursuits. Which is gonna backfire pretty soon. And this is as good an excuse as any for the cessation of such things: Starfleet knows it's stupid to keep doing it, but Starfleet also has dirt-cheap, surefire, available-to-all methods of going back in time to easily hunt down anybody who goes back in time against Starfleet's warnings!

. I was also thinking of the Bozeman, but the circumstances of their arrival is so damn confusing...and seems to be a predestination one as the universe doesn't change ala' "Yesterday's Enterprise"...sending them back would probably be too dangerous.

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Who says the Bozeman wasn't sent back eventually?

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I got the impression that they would not have sent the Bozeman back unless there was a critical need to do so, like say a war with the Klingons that put the Federation on the losing end ala the Enterprise-C.

That way, only certain knowledgeable people like Spock or Scotty could modify the BOP engines to do the same thing while other ships don't have this ability.

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So the mission to observe Earth in the 1960s was so super-secret that not even all that many in Starfleet were told of it?

Sounds a bit dubious, when we think how unimportant that mission appeared. Our heroes didn't exactly achieve anything they could plausibly have set out to achieve - they just had random adventures in the past. Why study the 1960s?

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They had cited a reason for the 1960s trip and it is entirely possible there were other missions carried out by other ships. And let us not forget about anyone stationed at the Guardian of Time could act as sentries for detecting major timeline changes.

But, what I was getting at based on Mytran's post was the idea that a ship must be modified in some way like with a unique intermix formula to be able to time travel otherwise we'd have lots of random cases where ships that got too close to a star and pulled away shot back (or forward) in time.

The knowledge that time travel is possible likely existed in TOS but the actual knowledge on how to do so probably was limited to a select few.

I thought they turned that cloaking device over to the Feds. I thought that was the whole point.

As for Post TNG eps where a crew was stuck after time-travelling. I was also thinking of the Bozeman, but the circumstances of their arrival is so damn confusing...and seems to be a predestination one as the universe doesn't change ala' "Yesterday's Enterprise"...sending them back would probably be too dangerous.

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Actually the situation in "Cause and Effect" is quite simple compared to "Yesterday's Enterprise." In YE, the "main" timeline turned out the way it did because the Enterprise-C's time travel was two-way -- they were taken into the future, saw how it turned out as a result of their disappearance at Narendra III, and went back again to defend the Klingon colony and thus avert the war, leading to the history we know. The situation in C&E is nothing more than the Bozeman effectively being stuck in stasis for 90 years and then coming out of it. It's not really time travel, more an elaborate form of time dilation. It was effectively a one-way trip as far as the rest of the universe was concerned, so there was no alteration of history; there was just the single history where the Bozeman disappeared in 2278 and reappeared in 2368.

So the mission to observe Earth in the 1960s was so super-secret that not even all that many in Starfleet were told of it?

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Well, maybe! Perhaps the race that Gary7 came from contacted Starfleet Intelligence in the 23rd century and requested that the Enterprise be despatched on this specific research mission. They would of course have foreknowledge of the outcome, but hey...

From a storytelling standpoint, later series had the holodecks. So they could do "time travel" episodes anytime they wanted, without the slingshot.

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Yeah, watching some of these old episodes makes me wish that they had better back lots when they were originally filming Trek. It's too bad they didn't have a Kubrick or Ridley Scott set to hijack every once in a while. Instead it was, "Ah yes, we're stuck in the old west... ...again."